1. Field of the Invention
The present invention relates to polyarylene ether for optical communications, and more particularly, to polyarylene ether used for manufacturing an optical communication device.
2. Description of the Related Art
A range of light wavelengths for optical communications has been shifted from 800 nm to 1,550 nm belonging to the wavelengths of near infrared light. Thus, it is ideal to manufacture an optical communication device using a material which barely absorbs light belonging to the wavelengths of near infrared light.
In general, a polymer is used for an optical substrate such as an optical lens or compact disk. Recently, research into use of such polymer as a material for an optical waveguide for light transfer in the near infrared range is being conducted.
However, a general polymer absorbs light of 1,000.about.1,700 nm in the near infrared range. Such absorption of near infrared light by the polymer is caused by overtone of harmonics according to stretching and deformation vibrations of carbon and hydrogen bond (C--H) in alkyl, phenyl and other similar functional groups. Thus, using the polymer as a material for an optical waveguide utilizing light in the near infrared range results in a large loss in light transfer. In order to reduce loss in light transfer, the light absorption wavelength of the polymer should be shifted from the wavelength region of the near infrared light to a longer or shorter wavelength region. To this end, a method for substituting hydrogen of the carbon and hydrogen (C--H) bond by fluoride (F) or heavy hydrogen (D) has been suggested.
In particular, the method for substituting the hydrogen of C--H bond by D is not suitable for a material for an optical communications device utilizing the light of 1,500 nm because the material having carbon and heavy hydrogen (C--D) bond absorbs much light of 1,500 nm. On the other hand, the method for substituting the hydrogen by F can minimize loss in light absorption at a wavelength of 1,000.about.1,700 nm.
Also, an optical material for manufacturing an optical device such as an opto-electronic integrated circuit (OEIC), an opto-electrical mixed wiring board (OEMWB), a hybrid integration device, a plastic optical fiber or a multi-chip module (MCM) requires thermal stability at 250.degree. C. lasting at least for 30 minutes. Because such thermal resistance of the optical material is very important, glass transition temperature, thermal decomposition temperature, thermal expansion coefficient and double refractive index of the optical material should be carefully considered.
A polyimide is widely known as a polymer having good thermal resistance. Because the polyimide has a resistance to heat at a high temperature, e.g., approximately 400.degree. C., great efforts are being made to utilize polyimide as a material for optical communications.
However, in general, polyimide has many C--H bonds within its molecule, loss in absorption of light is great at the near infrared region. To solve this problem, a polyimide whose hydrogen of C--H bond is partially or completely substituted for fluorine (F) has been reported. The polyimide whose hydrogen is partially replaced by F shows loss in light absorption of approximately 0.1 dB/cm at 1,310 nm, and the polyimide whose hydrogen is completely substituted by F barely shows loss in light absorption at 1,310 nm and 1,550 nm.
However, when substituting the hydrogen of C--H bond of polyimide by F as described above, the refractive index of the polyimide decreases. Here, the content of F in the polyimide is proportional to the decreased level of the refractivity index. Thus, because the polyimide whose hydrogen of C--H bond is replaced by F, i.e., fluorinated polyimide, has a low reflective index, the range of selection of a material capable of being used for cladding becomes narrow when the fluorinated polyimide is used as a material for the core of an optical fiber.
Also, the higher the fluoride content in the polyimide is, the lower the surface tension of the polymer is. Thus, it is difficult to coat such polymer on a substrate and a film formed of such polymer shows poor adhesion properties. As a result, film characteristics are lowered and the film is easily broken. Thus, actually, it is difficult to use the polyimide as a material for optical waveguiding.
Recently, poly(arylene ether) has been synthesized, which is a polymer having thermal resistance at a high temperature of approximately 400.degree. C. This polymer has excellent film processing characteristics and small dielectric constant and double refractive index. Due to such characteristics of polyarylene ether, the polyarylene ether is expected as a suitable material for a dielectric thin film required for manufacturing a semiconductor device.